Until recently, Fairy Bridge has been virtually unknown outside of China. It is located about 40 km northwest of Fengshan in northwestern Guangxi Province, China. The bridge is carved through the limestone karst by the Buliu River. Xianren Bridge, also known as Fairy Bridge, is the world's largest natural arch with a span measuring 400 feet or 120 meter. The following is a list of 10 biggest natural arches from around the world according to the Natural Arch and Bridge Society. As many as 2000 natural sandstone arches, including the world-famous Delicate Arch, in addition to a variety of unique geological resources and formations are found in this region. The Arches National Park in eastern Utah contains the largest concentration of significant natural arches in the world. Natural arches are abundant in the deserts of Utah and Arizona in the United States. Amidst this confusion new discoveries and potential candidates always keep popping up around the globe. Under these circumstances to prepare an irrefutable list of the world’s largest or longest or highest natural arch is impossible.
By contrast, the Dictionary of Geological Terms defines a natural bridge as a "natural arch that spans a valley of erosion." The correct method to measure an arch is also debated because of which the reported measurements often varies from source to source. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch that is primarily water-formed. The distinction between a bridge and arch is somewhat arbitrary. Some natural arch has a stream of water flowing underneath, in which case the arch is called a natural bridge. Text excerpted from "Highways in Harmony" publication produced by Historic American Engineering Record (HAER), in cooperation with the National Park Foundation.A natural arch is a geological formation where rocky cliffs subject to erosion from the sea, rivers or weathering forms a rock arch. Many bridges are curved or skewed, crossing a road or stream on a diagonal so as not to interrupt the flow of the roadway. Circular arches were employed for some narrower spans. The elliptical arch was occasionally used where there was sufficient horizontal clearance to carry the arch all the way to the ground, usually where the parkway intersected primary roads. Most were segmental arches rising from straight-sided abutment walls. As the parkway traverses several distinct geological areas over its nearly 500-mile length, the type and appearance of the stone used in the work varies from location to location.ĭifferent arch shapes were employed, the choice being dictated by the length of span and topographic conditions. In other cases, stone was obtained from rock cuts created during the construction of the roadway. The stone was generally obtained from quarries located near the construction site. The stone facing for these structures was a hallmark of the rustic style of architecture employed by the National Park Service, which dictate the use of materials that would enable structures to harmonize with their environments. Many underpasses bearing the parkway over other roads are stone-faced arch structures as well.
All but one of the overpasses, or grade separation structures carrying roadways over the parkway, are stone-faced arch structures. The stonework is not merely decorative, but serves as the form for the concrete frame. They were constructed by erecting stone arch rings, abutments and spandrel walls, then pouring concrete on a network of steel reinforcing rods. Many of the grade separation structures appear to be old-style stone arch bridges but are actually reinforced concrete structures. Bureau of Public Roads engineers and National Park Service landscape architects collaborated on the design of the parkway bridges. Many of these 168 structures have a rustic stone appearance that blends well with the mountain landscape others are sleek modern steel and reinforced concrete structures.
The most distinctive architectural feature of the Blue Ridge Parkway is its outstanding collection of bridges and grade separation structures, which allow the parkway to cross streams or pass safely over or under other roads.
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